The English native speaker teacher of a friend wrote the following question:

What role does reason and emotions play in sharing knowledge?

As far as I know, this question has a grammatical error, for the subject is plural: reason and emotions. So it should be:

What role do reason and emotions play in sharing knowledge?

However, I think that if his teacher had taken reason and emotions as one whole unit, then he could use does instead of do. I am not sure if that way of expressing the question would be idiomatic though.
Is the usage of does possible in this case, or is it just a grammatical error?

There's no real precedent to group reason and emotion as one thing. In fact they are often seen as opposites. I would say this is just a common error people make. There are two subjects, so it should be "do." In addition, I would change it to "emotion" not "emotions."
– KumaAraSep 11 '17 at 6:51

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I agree with KumaAra, above, additionally, I would change 'role' to 'roles', which underlines that 'reason' and 'emotion' are actually separate elements.
– Lee LeonSep 11 '17 at 8:01

The English of the English, even teachers, is not always good.
– Lee LeonSep 11 '17 at 8:48

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In the context, "reason and emotions" is considered a single causative factor, so singular verb is correct in that sense. Apropos @KumaAra -- it's true they are contradictory. However, the net effect is what comes into play.
– KrisSep 11 '17 at 10:37

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Easier cases to see the difference in agreement notional concord allows/demands are: 'Bacon and eggs are both to be found on aisle 17' / 'Bacon and eggs is my favourite meal for breakfast'. / Like KumaAra, I wouldn't use a singular verb here.
– Edwin AshworthSep 11 '17 at 10:44